Comparative Fish Parasite Dynamics in Urban and Peri-Urban Tributaries of Lake Victoria: Evidence from Clarias gariepinus in Kisumu, Kenya

This study provides a comprehensive comparative analysis of parasitic infections in Clarias gariepinus (African sharptooth catfish) sampled from the Kisat and Auji River mouths in Kisumu County, Kenya, both of which discharge into Lake Victoria. The research integrates parasitological assessments with ecological and physicochemical water quality analyses to investigate how environmental degradation influences fish health and parasite dynamics in freshwater ecosystems. Water quality measurements revealed notable differences between the two sampling sites. The Kisat River mouth exhibited moderately acidic conditions (pH 5.49–6.85), reduced dissolved oxygen concentrations (mean 4.19 mg/L), and significantly elevated turbidity levels (mean 89.90 NTU). These parameters are indicative of substantial organic pollution, high sediment load, and anthropogenic disturbance within the watershed. In contrast, the Auji River mouth demonstrated comparatively improved ecological conditions, characterized by higher dissolved oxygen levels and lower turbidity, suggesting reduced environmental stress. Parasitological examination of fish specimens identified a diverse assemblage of parasites, including protozoans, monogeneans, and nematodes. The most prevalent taxa included Ichthyophthirius multifiliis, Gyrodactylus spp., and Contracaecum spp., all of which are known to adversely affect fish health and aquaculture productivity. Infection prevalence was markedly higher in fish collected from the Kisat River mouth (87%) compared to those from the Auji River mouth (61%). This disparity suggests a strong association between degraded environmental conditions and increased susceptibility of fish to parasitic infections, potentially due to stress-induced immunosuppression. The findings highlight the critical role of environmental quality in shaping host–parasite interactions and underscore the need for integrated watershed management strategies. Effective pollution control measures, habitat restoration, and routine monitoring of fish health are essential to safeguard fisheries resources and maintain ecological integrity in Lake Victoria. This study contributes valuable insights into the linkages between environmental stressors and disease dynamics in tropical freshwater systems, with implications for sustainable fisheries management and conservation efforts.